Metal Dispersion Research Articles

Ceria-boosted Ni/Al2O3 catalysts for enhanced H2 production via acetic acid dry reforming

Acetic acid dry reforming (ADR) is a promising route for sustainable H2 generation. However, coke inhibition during ADR is the main challenge and not resolved by using suitable promoted catalysts. In this work, Ce promotion on 10%Ni/Al2O3 catalysts with 1-5 wt%Ce was evaluated for ADR at varied temperatures of 923–998 K and stoichiometric feed in a fixed-bed rig. CeO2 addition of 1–3% enhanced metal dispersion, and surface area whilst basic CeO2 character significantly boosted the concentration and density of basic sites on catalysts. Particularly, the CO2 uptake of promoted catalysts was about 2.49–3.73 times greater than that of counterpart sample. CH3COOH and CO2 conversions were enhanced with rising Ce loading and the highest reactant conversions were observed at 3 wt%Ce. The improved adsorption of acidic CH3COOH and CO2 molecules due to increasing amount of basic sites as well as redox attributes of CeO2 promoter could be responsible for the enhancement in ADR activity and yield of H2 and CO. The mechanistic two-step pathway for coke suppression induced by CeO2 promotion was elaborated in this work. Generally, carbonaceous species formation on 3%Ce–10%Ni/Al2O3 was considerably reduced about 1.6–2.0 times. H2/CO ratio varied from 0.59 to 0.65 relying on ADR temperature over 3%Ce–10%Ni/Al2O3. These H2/CO values, two times higher than theoretical H2/CO ratio in ADR, are compatible for downstream gas-to-liquid processes to selectively yield high molecular weight olefins. Water formation rate increased from 8.67 × 10−6 to 4.71 × 10−5molH2O gcat−1 s−1 with rising temperature within 923–998 K on 3%Ce–10%Ni/Al2O3.

Effect of cobalt on the activity of nickel-based/magnesium-substituted hydroxyapatite catalysts for dry reforming of methane

The dry reforming of methane (DRM) reaction can directly convert methane (CH4) and carbon dioxide (CO2) into syngas (H2+CO), which is a promising method for achieving carbon neutralization. In this study, a series of 3Ni-xCo/Mg1HAP alloy catalysts with different ratios were synthesized by the coprecipitation method, and the optimum Ni/Co ratio for the DRM reaction was studied. A series of characterization methods revealed that after Co was added, the formation of Ni–Co alloys increased the interactions between metals. However, an excess of Co inhibits the entry of Ni into the lattice of Mg1HAP, resulting in metal accumulation on the surface of the support. In addition, the introduction of Co improves the dispersion of Ni metal, which endows the catalyst with better catalytic activity and stability. Raman spectroscopy of the catalyst after the stability test showed that the addition of Co reduced the proportion of graphitic carbon, which was also the main reason for its improved stability.

Response optimisation of TiO2-supported bimetallic NiCo catalyst for the cracking and deoxygenation of waste cooking oil into jet-fuel range hydrocarbon fuels under non-hydrogen environment

Waste cooking oil is a sustainable feedstock that can be utilised to produce biojet fuel via the hydrodeoxygenation process. However, the need for hydrogen for the hydrodeoxygenation process incurs high cost. In the present work, a type of bimetallic catalyst that can deoxygenate and selectively crack free fatty acids under hydrogen-free conditions was developed. The NiCo/TiO2 catalyst was prepared via the impregnation of varying amounts of Ni and Co salts onto TiO2. Optimisation of the production conditions was performed via response surface methodology based on the Box-Behnken experimental design to maximise the deoxygenation and biojet fuel yield. A maximum deoxygenation yield of 83.13 % with 44.5 % biojet fuel selectivity was obtained from the experiment and optimisation based on Box-Behnken design (R2 > 0.9). Incorporation of Ni and Co onto TiO2 reduced the surface area of the catalyst, but active metal dispersion significantly improved the deoxygenation performance and biojet fuel selectivity. The viscosity, flash point, freezing point and net heat of combustion value of the liquid product were within the jet fuel standard specifications. Overall, the study shows the potential of bimetallic NiCo/TiO2 catalyst in waste cooking oil deoxygenation for biojet fuel production.

Cu0·1In0·01/S-1 catalysts with high efficiency towards methanol steam reforming

Cu0·1/S-1, Cu0·1Zn0·01/S-1, Cu0.1Inx/S-1 (x = 0.01, 0.03, 0.05) and Cu0·1Ce0·01/S-1 were successfully prepared with S-1 as the carrier material and applied to methanol steam reforming (MSR) reaction. To further explore its chemical and physical properties, XRD, BET, SEM-EDS, ICP, FTIR, H2-TPR, NH3-TPD, CO2-TPD, and Raman were used to characterize the synthetic S-1 zeolite catalysts. The measured physicochemical properties revealed that utilizing S-1 zeolite as the carrier effectively altered the size of the metal particles, enhancing their dispersion and reduction characteristics. Compared with five different types of S-1 zeolite catalysts, the Cu0·1In0·01/S-1 catalyst has a large specific surface area and pore size. It exhibited superior active metal dispersion, with the lowest reduction temperature for the active metal CuO. The catalyst also showed a high Lewis acid content on its surface, forming the In-Lewis acid site. Consequently, the Cu0·1In0·01/S-1 catalyst exhibits exceptional performance in methanol steam reforming for hydrogen production reactions. It exhibited the best performance with a methanol conversion rate of 100%, H2 selectivity of 100% under the conditions of 1 MPa, 250 °C, the S/C molar ratio of 2.5, and the WHSV of 0.5 h−1, which outperforms most of the reported catalysts in methanol steam reforming.© 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Enhancement of hydrogen-rich gas production by acetic acid steam reforming: characterization of Ni–Co modified biochar-based catalysts

Abstract The development of cost-effective and highly efficient biochar-based catalysts is essential for the catalytic steam reforming process of bio-oil. In this study, pickling peanut shell biochar was used to prepare biochar-supported Ni/Co monometallic catalyst and biochar-supported nickel-Co bimetallic catalyst through the impregnation method. The catalytic effect of these catalysts on acetic acid (a bio-oil model compound) steam reforming was investigated. It was found that Co could enhance the dispersion of metal particles. The catalyst exhibited the best catalytic effect and significantly improved resistance to carbon deposition with a loading of 8 wt% and a Ni-to-Co ratio of 6:2. At the temperature of 600 °C and the S/C ratio of 3, the selectivity of H2 reached 84.48 %, and the conversion of acetic acid reached 95.49 %. A synergistic effect was observed between Ni and Co, leading to increased metal dispersion, enhanced reducibility, and a higher number of active centers. Co facilitates water dissociation and promotes the oxidation of C–H and mobile O, resulting in a faster decarbonization rate. The effective utilization of biochar-based catalysts and the rational utilization of bio-oil contribute to the timely achievement of carbon emission reduction targets.

Unraveling the mechanistic interplay between CO and CO2 hydrogenation over Ni, Co, and NiCo catalysts

Although CO and CO2 hydrogenation reactions have been extensively studied, there is still significant controversy regarding the mechanism of methane formation and the routes for byproducts, especially when both carbon sources are simultaneously present. This work combines kinetic, operando-spectroscopic, isotopic techniques and DFT calculations to elucidate the relationships between CO and CO2 hydrogenation over mono Ni, Co and bimetallic NiCo catalysts with similar metal dispersion. The bimetallic catalysts showed a slight synergistic effect for methane formation from CO, while from CO2 the effect was opposite, showing a negative shift of activity as compared with those observed on the monometallic catalysts. The kinetic analysis shows similar apparent order with respect to H2 (∼0.5) and an inverse secondary isotope kinetic effect (<1) for both methanation reactions, suggesting that CH4 formation proceeds via C-O bond breaking in an H*-assisted mechanism, where the rate-determining step was not shown to be sensitive to the carbon source. The anti-synergistic effect observed on the bimetallic catalysts during CO2 hydrogenation is explained by the formation of unreactive HCOO* species (spectator), which generate a lower density of methane intermediates. On the other hand, the formation of the undesired products, i.e., CO or CO2 during CO2 or CO hydrogenation, respectively, shows relevant differences since the CO formation during CO2 hydrogenation proceeds through the desorption of the carbonyl species adsorbed on weak sites, meanwhile the CO2 formation from CO hydrogenation is due to a minority route of direct dissociation of CO, allowing the rejection of O* with CO* to produce CO2. This study contributes to elucidate the routes that determine the selectivity and reactivity for CO and CO2 hydrogenation and their mechanistic relationship. This information is valuable for the rational design and development of new materials with high performance during hydrogenation processes.

Morphology effects of CeO2 on the performance of CaO-Cu/ CeO2 for integrated CO2 capture and conversion to CO

CeO2 support inhibits CaO sintering, and oxygen vacancy influences CO2 hydrogenation performance, making CeO2 widely applied in Integrated CO2 capture and in-situ conversion technology for reverse water–gas shift (ICCC-RWGS). Oxygen vacancy concentration was dependent on the morphology of CeO2, which would affect metal dispersion and CO2 hydrogenation conversion. However, Very little is known about the morphology effect of CeO2 on the carbon capture and in-situ hydrogenation performance of DFMs. Here, Cu/CeO2 with different CeO2 morphologies was synthesized, and high Cu dispersion was achieved on Cu/CeO2-R, exhibiting the best CO2 hydrogenation performance. Integrated Cu/CeO2 with CaO by physical mixing method, CaO-Cu/CeO2 was used to investigate the morphology effects of CeO2 on the performance of CaO-Cu/CeO2 for integrated CO2 capture and conversion to CO. CaO-Cu/CeO2-R exhibited the best capture-hydrogenation performance (CO2 conversion rate of 75 %, CO production rate of 9.72 mmol/g). The CeO2-R provided more surface oxygen vacancies, enhancing carbonate hydrogenation. The larger specific surface area and {110} crystal plane of CeO2-rod enhanced Cu dispersion, and the smaller particle size of CeO2-R enhanced its interaction with CaO, improving the cyclic stability of CaO-Cu/CeO2-R. The hydrogenation performance of CaO-Cu/CeO2 was dependent on the morphology of CeO2, providing insights into the design of high-activity metal catalytic components in ICCC-RWGS.

Induced π–complexation properties of smectites impregnated by Ni, Cu and Ag transition metals: The highly efficient styrene uptake

Two natural smectite minerals (montmorillonite and beidellite) differing in structural charge location were impregnated with varying amounts of transition metals: Ni(II), Cu(I) or Ag(I). The modification aimed to increase the affinity of the minerals towards styrene vapors. The structure, texture, chemical composition and surface chemistry of the materials were studied by XRD, FTIR, Raman, N2 adsorption/desorption, XRF and XPS. The experiments examined the influence of the starting smectite and the type of introduced metal on styrene adsorption efficiency. The styrene uptake mechanisms were investigated through solid state analysis and supported by DFT calculations. The study demonstrated that the small content of introduced metals (<2% wt.) substantially increased styrene uptake (∼200–350% wt.) surpassing values reported for surfactant-intercalated smectites (∼40–80% wt.) and activated carbons (∼30% wt.). This enhancement was attributed to the π-complexation between dispersed d-block metals and π-electron-rich styrene molecules, subsequently leading to polystyrene formation. The DFT calculations were consistent with experimental findings, indicating a higher affinity of the raw beidellite towards styrene than the raw montmorillonite connected to the charge location. Moreover, the observed trends in calculated adsorption energies and lengths of weak hydrogen bonds allowed to explain a significant adsorption increase observed for the Ni- and Cu-impregnated montmorillonite-based materials.

Electrodeposition of Ni/Cu Bimetallic Conductive Metal-Organic Frameworks Electrocatalysts with Boosted Oxygen Reduction Activity for Zinc-Air Batteries.

Zinc-air batteries employing non-Pt cathodes hold significant promise for advancing cathodic oxygen reduction reaction (ORR). However, poor intrinsic electrical conductivity and aggregation tendency hinder the application of metal-organic frameworks (MOFs) as active ORR cathodes. Conductive MOFs possess various atomically dispersed metal centers and well-aligned inherent topologies, eliminating the additional carbonization processes for achieving high conductivity. Here, a novel room-temperature electrochemical cathodic electrodeposition method is introduced for fabricating uniform and continuous layered 2D bimetallic conductive MOF films cathodes without polymeric binders, employing the organic ligand 2,3,6,7,10,11-hexaiminotriphenylene (HITP) and varying the Ni/Cu ratio. The influence of metal centers on modulating the ORR performance is investigated by density functional theory (DFT), demonstrating the performance of bimetallic conductive MOFs can be effectively tuned by the unpaired 3d electrons and the Jahn-Teller effect in the doped Cu. The resulting bimetallic Ni2.1Cu0.9(HITP)2 exhibits superior ORR performance, boasting a high onset potential of 0.93V. Moreover, the assembled aqueous zinc-air battery demonstrates high specific capacity of 706.2mA h g-1, and exceptional long-term charge/discharge stability exceeding 1250 cycles.

Combined Approaches for the Remediation of Cadmium- and Arsenic-Contaminated Soil: Phytoremediation and Stabilization Strategies

The prolonged duration of phytoremediation poses a risk of heavy metal dispersal to the surrounding environment. This study investigated a combined remediation approach for cadmium (Cd)- and arsenic (As)-contaminated soil by integrating phytoremediation with stabilization techniques. Bidens pilosa was utilized as the phytoremediator, and steel slag, pyrolusite, and FeSO4 were employed as stabilizing agents in the pot experiments. Key metrics such as soil moisture content, root length, plant height, and heavy metal concentrations in Bidens pilosa were measured to evaluate the remediation efficacy. Additionally, the bioavailability, leaching toxicity, and chemical forms of Cd and As, along with other soil properties, were analyzed. The results indicated that the optimal restoration effect was achieved by combining steel slag, pyrolusite, and FeSO4 with stabilizers in a ratio of 2:1:10. Additionally, the optimal dosage of these materials was found to be 9% by weight. Mechanistic studies, including heavy metal speciation analysis, X-ray photoelectron spectroscopy (XPS), and microbial community diversity analysis, revealed that the stabilization effects were primarily due to the interactions of anionic and cationic ions, chelation by organic acids secreted by plant roots, and enhanced microbial activity. A cost–benefit analysis demonstrated the technical, economic, and commercial viability of the combined remediation approach.

Anchoring Metal-Nitrogen Sites on Porous Carbon Polyhedra with Highly Accessible Multichannels for Efficient Oxygen Reduction.

Transition metal-nitrogen-carbon complexes, featuring single metal atoms embedded in a nitrogen-doped carbon matrix, emerge as promising alternatives to traditional platinum-based catalysts, offering cost-effectiveness, abundance, and enhanced catalytic performance. This work introduces a novel method for the etching and doping of zeolitic imidazolate frameworks (ZIFs) with transition metals, creating a uniform distribution of secondary metal centers on ZIF surfaces. By disrupting the crystalline symmetry of ZIFs through synthetic defect engineering, we gain access to their entire internal volume, creating multichannel pathways. The absorption of metal ions is theoretically simulated, demonstrating their thermodynamically spontaneous nature. The selective removal of defect channels under Lewis acidic conditions, induced by metal ion alcoholysis/hydrolysis, facilitates the introduction of metal atoms into ZIF cavities. The resulting single-atom catalyst, after pyrolysis, features a three-dimensional (3D) multichannel structure, high surface area, and uniformly dispersed metal atoms within the N-doped carbon matrix, establishing it as an exceptional catalyst for the oxygen reduction reaction (ORR). Our findings highlight the potential of using metal etching in defect-engineered metal-organic frameworks (MOFs) for single-atom catalyst preparation, paving the way for the next generation of high-performance, cost-effective ORR catalysts in sustainable energy systems.

Upcycling of waste acrylonitrile butadiene styrene as N-doped carbocatalyst for peroxymonosulfate-induced degradation by solvothermal process

Advanced upcycling of post-consumer waste plastics into functional carbocatalyst has emerged rapidly as a strategy for simultaneously achieving waste plastics disposal and alternative catalysts fabrication. In this study, this type of magnetic N-doped carbocatalyst hybrid was fabricated by a facile solvothermal impregnation of metallic nitrates into waste acrylonitrile butadiene styrene polymer. The key point of the process was that solvothermal impregnation remarkably enhanced a homogeneous metal dispersion and graphitic N structure was stably introduced into carbocatalyst due to N heteroatoms in inherent structure of waste plastics. It was found that carbocatalyst with predominant encapsulation of magnetic CoFe2O4, Fe0.64Ni0.36 and CoFe possessed excellent catalytic performance to activate peroxymonosulfate with substantial degradation of 98.3% synthetic azo contaminant. Mechanism study indicated that graphitic N and metal species exhibited strong synergistic effects for peroxymonosulfate activation to generate SO4·−, ·OH and 1O2. This system achieves a dual-pathway degradation and electron transfer from azo contaminant to peroxymonosulfate to dominate degradation of azo contaminant, providing a new insight into magnetic carbocatalyst confinement from plastic scrap for peroxymonosulfate activation and its versatile application in wastewater reclamation.

Efficient CoCu/SiO2 Catalyst Derived from Co(Cu) Silicate for Aqueous‐Phase Furfural Hydrogenation

AbstractConverting the abundant biomass resources in nature into fine chemicals can not only reduce carbon emissions but also effectively deal with the depletion of fossil energy, which is of strategic significance for sustainable development. In this paper, by optimizing the content of bimetallic components, highly active co‐doped Co1Cu3 bimetallic silicate was designed and synthesized. After reduction, a highly dispersed and stable Co1Cu3/SiO2 catalyst was obtained, which was used to catalyze the aqueous phase hydrogenation of furfural (FFR) to cyclopentanone (CPO). Compared with the traditional supported catalyst, the Co1Cu3/SiO2‐ammonia evaporation (AE)‐300 catalyst prepared by AE has the best performance. Under the optimal reaction conditions, the conversion of FFR was as high as 95.1 % and the selectivity of CPO was 88.6 %. This high activity can be attributed to the formation of highly dispersed and uniform metal active sites with low content of Co. At the same time, the formation of flocculent silicate enhances the synergism between CoCu and SiO2 support and increases the specific surface area of the catalyst. In addition, the experimental results show that the reaction carbon balance will be destroyed with the high concentration of FFR solution.

(Invited) Graphene-Supported Fe/Ni Single Atoms and Feni Alloy Nanoparticles as Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc-Air Batteries

To alleviate the severe energy crisis and environmental problems caused by the massive and unsustainable consumption of fossil fuels, it is urgent to develop renewable energy conversion and energy storage technologies to reform the traditional energy structure. Batteries are considered as one of the most promising energy storage technologies due to their sustainability, high efficiency and less pollution. Among various battery storage devices, rechargeable zinc-air batteries (ZABs) have attracted widespread attention on account of their high theoretical energy density (1086 Wh kg– 1), low cost, abundant zinc resources, low operating temperature, and good stability and safety in aqueous environments. However, the kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurred on the air electrode during the discharging and charging processes are extremely sluggish, leading to low energy efficiency, which significantly limits the large-scale application of rechargeable ZABs. Pt-based electrocatalysts exhibit high ORR activities, while Ru- and Ir-based oxides are excellent OER electrocatalysts, but natural scarcity, high cost and poor durability seriously reduce the marketability and commercial competitiveness of rechargeable ZABs. Therefore, the development of robust, cost-effective and high-efficiency non-noble metal bifunctional ORR/OER electrocatalysts is of crucial significance for the practical application of rechargeable ZABs.As a promising alternative, earth-abundant transition metal (Fe, Co, Ni, etc.)-based materials have been extensively studied due to their relatively high electrocatalytic activity and durability. Thereinto, transition metal and nitrogen co-doped carbon (M-NC), especially Fe-NC, has been demonstrated to be the most effective ORR catalyst, and the active sites are generally considered as atomically dispersed metal coordinated to N atoms (M-Nx sites, x indicates the number of N atoms coordinating the metal). Nevertheless, M-NC catalysts only possess good ORR activity with poor OER performance. Bimetallic FeNi nanocomposites (metals, oxides, carbides, sulfides) are promising for OER. At high potentials, highly active FeNi oxyhydroxide species are generated on the surface of the FeNi-based electrocatalysts. Since ORR and OER depend on different catalytic active sites, an ideal bifunctional oxygen electrocatalysts should integrate M-NC complex with high ORR activity and bimetallic FeNi nanocomposite with a high OER activity to achieve bifunctionality. However, due to the intense competition between transition-metal single atoms and nanocomposites in the preparation process, it is challenging to combine them properly for superior bifunctional ORR/OER catalytic activity.Herein, we report a bifunctional oxygen electrocatalyst consisting of ZIF-derived carbon-anchored Fe/Ni single atoms and FeNi alloy nanoparticles; meanwhile, graphene is also introduced as carbon support to improve the uniformity of active sites (denoted as Fe/Ni-NC||FeNi@G). Benefiting from this unique composition and structure, Fe/Ni-NC||FeNi@G electrocatalyst displays excellent bifunctional ORR/OER activity and durability in rechargeable ZABs. This work provides an effective approach to designing highly efficient non-noble metal multifunctional catalysts for practical applications in rechargeable metal-air batteries. Acknowledgements Thanks for the financial support from the Shenzhen Science and Technology Innovation Committee (JCYJ20180507183818040).

(Invited) Tuning Selective CO2 Electrohydrogenation Under Mid Temperature and Pressure

To address rising environmental concerns and energy challenges, it is highly desirable to develop green technologies for a sustainable future. Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds. Electrochemical CO2 hydrogenation using renewable electricity is considered one of the most promising pathways to reach the environmental economics. Among various electrochemical devices, a solid state electrolyzer working at intermediate temperatures has the advantages of high reaction rates and low overpotentials. As CO2 molecules is quite stable, it is critical to develop electrocatalysts with high activity to reduce electricity engagement. Also, CO2 hydrogenation has multiple pathways which normally results in low selectivity for a target product. A tunable electrocatalyst with high selectivity to different products is desirable for CO2 conversion reactions. Heterostructured nanomaterials attracts great attentions in electrochemical systems. With careful design, they can show very high activity and selectivity towards an electrochemical reaction pathway. In this work, we combine theoretical simulations, including density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations, with experimental methods (characterizations and electrochemical measurements) for rational design of highly efficient heterostructured nanomaterials for CO2 hydrogenations. We studied the strong metal-support interaction (SMSI) in a doped CeO2 supported noble metal nanoparticles (NPs) system using theoretical calculations. The results indicate that SMSI largely depends on chemical conditions of the support and particle size of dispersed metal NPs. By tuning the SMSI, we can successfully change the catalytic activity and selectivity towards CO2 hydrogenation reactions. Based on these findings, we designed tunable heterostructured nanomaterials for efficient hydrogenation reactions at intermediate temperatures. These predictions were further confirmed by experimental method. By using a combination of high-throughput theoretical calculations and electrochemical measurements, we successfully developed highly active catalysts for electrochemical CO2 hydrogenation reactions. This framework is also applicable to other electrochemical systems using heterostructured materials.

Single Atom Platforms on Surfaces: A Step Towards Future Catalysts

Single (metal) atoms (SAs) have attracted great attention in virtue of their intriguing physical and chemical properties, representing a fertile playground for fundamental studies of electronic, magnetic and chemical phenomena. Placing SAs on clean, crystalline and atomically flat substrates allows the study of their properties and functions via the whole plethora of surface science tools, offering direct access to their features with ultimate resolution. Moreover, the isolated metal atoms exhibit peculiar properties and tend to behave similarly to reactive centres in solution or gas phase, bridging homogeneous and heterogeneous catalysis. In these regards, atomically dispersed metal catalysts (ADCs) have recently received great attention [1, 2]. However, they suffer some intrinsic bottlenecks such as a poor tunability and limited maximum density.Here we show the successful achievement of single atom platforms (SAPs), where SAs are coordinated to atomically precise organic templates, confined to a two dimensional surface. The templates are obtained via the on-surface synthesis (OSS) of carefully designed molecular precursors, and consist of carbon-based, covalent polymers equipped with side moieties that act as coordination sites. These groups capture metal atoms that are deposited on the substrate in a post-synthetic step, and together form active site with rich potential applications. Conceptually, the obtained SAP offers rich tunability prospects by varying not only the substrate and the SA, but also the organic ligand. Its shape and composition (e.g. heteroatoms, functional groups, strain, etc.) will influence the properties of the SA and enable their fine tuning. Moreover, the versatility of the OSS strategy offers a wide plethora of possible architectures, allowing also the precise modification of the SA density.We have characterized each stage of the SAP preparation via high-resolution scanning tunnelling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) with functionalized tips [3]. The trapping and conversion ability of these well-defined active sites towards CO and CO2 was then studied. Our investigation allows the direct visualization of reactants and binding motifs with unprecedented resolution, and opens new avenues for the study of chemical reactions localized at the active sites of our SAP.[1] Wang, A.; Li, J.; Zhang, T. Heterogeneous Single-Atom Catalysis. Nature Reviews Chemistry 2018, 2 (6), 65–81.[2] Hannagan, R. T.; Giannakakis, G.; Flytzani-Stephanopoulos, M.; Sykes, E. C. H. Single-Atom Alloy Catalysis. Chem. Rev. 2020, 120 (21), 12044–12088.[3] Gross, L.; Mohn, F.; Moll, N.; Liljeroth, P.; Meyer, G. The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy. Science 2009, 325 (5944), 1110–1114. Figure 1. Single atom platform concept. Sketch of surface-adsorbed single atoms (orange dots) and of a single atom platform. Here, the organic part is represented by 1D polymers adsorbed on a surface, and the single atoms decorate the coordination sites (U-shaped motifs). Figure 1

Efficient hydrolytic dehydrogenation of ammonia borane catalyzed by ultrafine Pt clusters confined in Ni–Ti layered double hydroxides with closo-dodecaborate

Ammonia borane (NH3BH3, AB) is a highly promising candidate for hydrogen storage. Nevertheless, there is an urgent need to develop an efficient and stable catalyst that can control hydrogen generation under mild conditions. The use of catalysts with numerous surface atoms anchored to a carrier to achieve a synergistic effect is an appealing approach in catalysis. In this work, a series of highly dispersed metal clusters NiTi-LDH@B12H12@M (M = Au, Pd, Pt, Ag) catalysts were successfully synthesized at room temperature by leveraging the reductivity of [closo-B12H12]2- immobilized in the layered double hydroxide (LDH) laminate, along with the spatial confinement and anion exchange capabilities of LDH. Specifically, utilizing the optimal catalyst NiTi-LDH@B12H12@Pt 2.4% (wt. Pt), the AB hydrolysis reaction exhibited extraordinary catalytic activity. It exhibited a first-order reaction rate with respect to Pt and a near zero-order reaction rate with respect to AB concentration. The AB hydrolysis can be achieved in a mere 29 s at 25 °C with a conversion rate of 100%. The corresponding turnover frequency (TOF) attains a value of 454.06 molH2molPtmin−1, and the apparent activation energy (Ea) is 41.8 kJ mol−1, surpassing numerous previously reported Pt-based catalysts. The outstanding catalytic performance can be ascribed to the uniform distribution of ultrafine Pt clusters, along with the synergistic effect conferred by NiTi-LDH and intercalated anions ([closo-B12H12]2-).

Modulating nickel precursors to construct highly active Ni/Y2O3 catalysts for CO2 methanation

Constructing the interface of Ni/Y2O3 heterogeneous catalyst is a feasible strategy for efficient catalyst design in CO2 methanation, which can create the active Y–O–Ni interfacial sites by utilizing the interaction between Ni and Y2O3. In this work, the strategy of using different nickel precursors (nickel nitrate, nickel acetate, basic nickel carbonate and nickel citrate) was used to prepare various Ni-based catalysts supported on Y2O3, which were estimated for their catalytic performance on CO2 methanation. The catalysts were characterized based on BET, XRD, TEM, H2-TPR, XPS and CO2-TPD, etc. The results indicated a close correlation between the metal dispersion and particle size of Ni/Y2O3 catalysts and the nickel precursor employed. The Y–O–Ni interface structure in Ni/Y2O3 catalysts, associated with basic sites, provides a richer source of basic sites, offering more active sites for CO2 adsorption and activation. Ni/Y2O3 catalyst prepared with nickel nitrate as the precursor exhibited characteristics such as a highly enhanced nickel dispersion, a smaller nickel particle size, and more abundant metallic Ni0 sites. Moreover, nickel nitrate-derived Ni/Y2O3 catalyst exhibited optimal catalytic activity, achieving a CO2 conversion rate of up to 92 % at 300 °C, with 100 % selectivity to CH4, and displaying good stability over 30 h. Therefore, the dispersion of Ni and the size of Ni particles could be controlled by adjusting the precursor, which is closely associated with the catalytic activity of Ni/Y2O3 catalyst. This work unveils the interface-property relationship of Ni/Y2O3 catalysts and provides a new insight into strategy of constructing more effective Ni-based catalyst for CO2 methanation through the controlled nickel precursor.

Surface property tuning of LaCr0.7Ni0.3O3 based perovskite catalysts enable efficient operation of SOFCs on liquid fuels

A-site Sr or Ca substituted perovskite LaCr0.7Ni0.3O3 (LSCN, LCCN) are prepared in this work as catalysts of simulated diesel fuel (N-hexadecane) steam reforming for the on-board hydrogen supplement of solid oxide fuel cells (SOFCs). The effect of different dopants on active metals dispersion and surface properties on catalyst performance is analyzed. The results of the investigation reveal that LCCN possesses the highest catalytic activity coupled with exceptional stability, achieving full fuel conversion at WHSV = 5 mL/g·h, S/C = 3.0, and 750 °C and keeping stable for 200 h, thereby emerging as a potential candidate for liquid fuel processing. SEM, H2-pulse chemisorption and XPS results confirm that the excellent performance is due to the high metal dispersion and steam activation capacity. The poor catalytic performance observed in LSCN is primarily attributed to the presence of Sr segregation and the formation of the SrCrO4 second phase. Sr segregation decreases the steam activation ability of the catalyst as confirmed by XPS. DFT calculation also shows that Sr dopant and Sr segregation decrease the exsolution trend of metal Ni in the perovskite matrix, leading to poor metal dispersion. A simulated reforming gas is used in SOFC and the cell can keep stable for 120 h at a discharging current density of 0.4 A/cm2. This study analyzes the difference between Ca and Sr dopants, and reveals the detrimental effect of Sr segregation, which could enlighten the effect of surface tunning on the performance of perovskite catalysts.

Single atom catalyst induced by redox reaction between iron ion and aniline monomer

The effective design of a low-cost, efficient, and stable non-noble metal electrocatalyst to substitute the noble metal electrocatalyst for oxygen reduction reaction is highly significant. Even though atomically dispersed metal catalyst shows excellent catalytic activity with maximized atom efficiency, the challenge often lies in achieving uniform distribution for single-atom catalysts owing to their tendency to aggregate. In this work, we present a sequential method that involves the reduction of iron (Fe) mediated by aniline (anchored on support), followed by pyrolysis to fabricate the Fe-Nx moieties and achieve the high density of single atom active sites. The resulting Fe SA 900 catalyst exhibited a half-wave potential of 0.84 V vs. reversible hydrogen electrode (RHE) for oxygen reduction reaction and outstanding stability in alkaline condition. Using various analysis techniques and electrochemical analysis, we demonstrated that the electrocatalytic activity of the catalyst arises from Fe single atom. To validate the practical applicability of Fe-N-C catalysts, we conducted an anion exchange membrane fuel cell (AEMFC) test, which demonstrated a high performance of 212 mW cm−2 at maximum power density. This study proves that the effectiveness of a sequential strategy adopting redox reaction and following pyrolysis for precise synthesis of a single atom Fe catalyst.